Heating device for electric discharge tubes



May 27, 1952 P. LEMAIGRE VOREAUX HEATING DEVICE FOR ELECTRIC DISCHARGE TUBES Fi1ed Jan. 11, .1949

Patented May 27, 1952 HEATING DEVICE FORELECTRIC DISCHARGE TUBES Pierre Lemaigre-Voreaux, Paris, France, assignor to Societe Anonyme pour les Applications de 1Electricite et des Gaz Rares-Etablissements v Claude-Pu et Silva, Paris, France Application January 11, 1949, Serial No. 70,170 In France February 13, 1948 2 Claims.

This invention relates to improvements in electric discharge tubes filled With rarefied gas and metaliic vapor in which the current of the discharge includes a unidirectionai component.

It is well known, for instance, that when a fluorescent lamp filled with rarefied gases and mercury vapor, designed for working on alternating current, is used on direct current without switching off for several periods of ten hours, it practically no longer has a lighting effect over a portion of its length beginning at its anodic extremity and extending over a length that. the longer the lamp and the larger the diameter, will be all the greater. This drawback is caused by the phenomenon known as cataphoresis that decreases progressively the homogeneousness of the the gaseous filling of the fluorescent lamp, and, in a general way, of the discharge tubes containing at one and the same time at least on rare gas and one metal1ic vapor and in which more current fiows in one direction than in the other.

The principal object of the invention is to provide electric discharge tubes in which the whole length of the positive column emits substantially evenly the desired radiation even when they work for a very long time, without switching 011, on

"a current including a unidirectional component.

An important feature of the invention relates to the use Of the heat originating in a resistor used for baflasting the tube, for heating a certain length of this tube on the side of the cathode, this length, measured from the faraday dark space, being at least equal to a tenth of the length between electrodes, but not extending appreciably beyond a point situated at a distance from the anode equal to 5 times the diameter of the tube and even, preierably. to times this diameter. Said cathode and said anode may have the same structure, but that electrode wi11 here be termed cathode which, due to the unidirectiona] component of the current, plays the part of a cathode more than of an anode, the anode being the other electrode. When the feed current ispurely unidirectional, the cathode plays only the part of a cathode and the anode only the part of an anode.

It has been found that the discharge tubes employed with this device remain luminous over the whole length of their positive column. The heated area must not extend too near the anode since then the dark anodic area reappears; a length equal to 5 times the diameter of the tube may be prescribed as a minimum for the nonheated anodic length. Preferably. the heated length extends over all the length of the tube,

2 except the cathode" and its immediate neighborhood that are heated by the cathodic drop, and stops at a distance from the anode equal to about 10 times.the diameter of the tube.

This heating may not be, besides, so strong as to prevent the condensation oi the mercury in the heated area, since this condensation proves by itself no drawbaek from the point of view of cataphoresis. The exact limits of length of a given type of tube that it is necessary tu heat depend, among others, on the sizes of the tube. on the gaseous filling, on the design of the electrodes, and on the form of the discharge current when the tube is traversed by an undulatory current; that is why no general rule can be given. These limits are, on the other hand, found easiiy by trials lasting for several periods of ten hours, carried out on a small number et tubes of this type. Some numerical examples are given later on.

Other objects and advantages of the invention will become apparent as the description proceeds.

Referring to the drawing:

Figure 1 is a sectionai view of a heating device embodying the invention, on the line ll of Fi ure 2.

Figure 2 is a sectional view, on the line 22 of Figure 1.

The lamp 3 is of a standard mode], started by preheating its thermoemissive electrodes that are heated by the discharge during working; these electrodes l0, Il are 52 centimetres apart and are identical, the lamp being of a model intended for working normally on alternating current. This lamp has an internal diameter of 3.5 centimetres and it is supported by the two caps 4 inserted in sockets 5 forming portion of a wireway 6 that encloses the resistance 1 constituting a part for ballasting the discharge. The distance between these sockets is 58 centimetres. The lamp takes 30 watts and it is fed by a 110 volts, direct current network; its starting by preheating is ensured by the relay 8 housed in the wireway; the relay 8 comprises, as is known, for instance a reactance and a glow switch with bimetaflic electrodes mounted in series, not shown. The envelope of this lamp contains argon with a pressure of 3.5 mm. and a small drop of mercury. Its operating current and voltage are respectively 0.5 amp. and 57 volts.

The value when warm of the ballasting resistance is ohms. This resistance is housed in the portion of the wireway situated above the electrode Il.) connected to the negative pole of the supply, therefore playing the part of cathode.

The wa1l of the wreway situated between this resistance and the lamp s drlled wth holes 9 and the resstance extends over a length of 17 centimetres, starting straight over th cathode. As the distancebetween the latter:and the faraday space is 2 centimetres, the*heated portion of the tube is equal to 0.3 time the length between electrodes; the heated portion finishes a t 35 centimetres from the anode H, therefore a12..

10 diameters from this electrode.

For a lamp of similar construction but of 118 centimetres of length betweenelectmdesz1; 110

volts operating voltage, a lengthbf 8&tefitimetrxs from the cathode is heated.

What I daim is:

1. In combination, an electqyic discharee tubecomprising an envelope filled with r arefiedgas and metalfic vapor and two main electr0dS. a cathode and an anode, the distance between the cathode and the anode beng longer than ei'ght-timesthe diametenof the envelope, a.sour cf eectriccurrent for;said tube, and uballasting meansconnected betweensaid source and said tube, and comprising heating resistor 1ocated close to the eni1ope cf saidtube, said resstor extezi i ng-- along said-genvelone atleastbetween, on; one si ie t11e'faraday darkspaceof thecath ode of said-tube whensaid-tube is bengsupplied With electric-current-bzsaid source througb said ballasti ng; means; and, entheotherside,apoint ofsaid enelope situated =at a distance romsaid dark space equal to at least one tenth 01" the length between said cathode and said anode/ and tp aticast twioe the-diameter of said envelope but-notxtending a;ppreeia5bl ybeyond a point situated;at-a distane-mm said anode said tube and -comprising a heatng resistor located close to the envelope of said tube, said resistor -extending along said envelope at least between, on;on;e side, the faraday dark space of the cathode of ssaid tube when said tube is being wsupplied with electric current by said source through said ballasting means, and, on the other side, a. point of said envelope situated at a distance r0m said dark space equal to at least one tenth of the length between said cathode and said anode, and to at least twice the diameter of said. enlope but not extendng appre ciably beyond a;point: s ituatedat a;distancefrom said anod e malt0 -te.n; ,times, e iam t r ai envelope., r v

' B ERRE' MAIGRE R' AU RFRENCES CITED The following references are of record: in the fi1e ofzthisL patent;

UNITED STATES PAIENTS' Nuxnber Name Date 16 68 Inman -,---,,1.+- Ma 10.1 2,398,111 Noel Apr; 9; 1946 2,404,002 Smith July l, 1946 2,448,937 Walter Sept; 7, 1948 

